The present invention relates to a device and a method for optically inspecting a connection between a connecting end portion of an electrode plate and a current collector plate in a sealed rechargeable battery electrode plate-connected structure.
A sealed rechargeable battery or a secondary battery such as a nickel cadmium battery or a nickel metal hydride battery includes an electrolyte, a positive electrode plate-connected structure, and a negative electrode plate-connected structure, which are sealed in a battery case. The positive electrode plate-connected structure includes a plurality of rectangular positive electrode plates connected to a positive electrode current collector plate. The negative electrode plate-connected structure includes a plurality of rectangular negative electrode plates connected to a negative electrode current collector plate. The positive electrode plate and the negative electrode plate are alternately stacked one upon another. An insulative separator is arranged between adjacent electrode plates. Electrode plates having the same polarity are arranged in parallel at constant intervals. The electrode plates each have an edge (connecting end portion). In a state in which the edge is in contact with the associated current collector plate at a right angle, the electrode plate is brazed or welded and integrally connected to the current collector plate.
FIG. 10 shows connection portions of the electrode plates in one electrode plate-connected structure. As shown in FIG. 10, the electrode plate-connected structure includes a plurality of electrode plates 10, and a current collector plate 11. Flanges project from opposite ends of the current collector plate 11. The plurality of electrode plates 10 are arranged facing toward one another in a state spaced apart from one another. One edge (connecting end portion) of each electrode plate 10 is brazed or welded and connected to the surface of the current collector plate 11 (also referred to as current collector plate surface) at plural locations. In the example of FIG. 11, each electrode plate 10 is connected to the current collector plate 11 at five connection portions. At the connection portion of each electrode plate 10, brazing filler material covering the surface of the current collector plate 11 is melted and subsequently solidified to form a fillet 12. Thus, the current collector plates 11 are adhered to the major surface of the associated electrode plate 10 by the fillets 12. That is, the fillets 12 join the electrode plates 10 and the surface of the current collector plate 11.
Each fillet 12 is formed between two adjacent electrode plates 10 and between the outermost electrode plate 10 and the flange of the current collector plate 11. The fillet 12 is filled in a corner that is formed by the current collector plate 11 and the corresponding electrode plate 10 that is in contact with the current collector plate 11. Further, the fillet 12 has a depressed surface curved into a U-shape between the two adjacent electrode plates 10.
If the formation of some of the fillets 12 is incomplete, the connection strength of the electrode plate 10 to the current collector plate 11 may be insufficient. In such a case, the electrode plates 10 may be separated from the current collector plate 11 due to an impact or the like. The connection state of each electrode plate 10 and the current collector plate 11 is thus inspected before sealing the manufactured electrode plate-connected structure in an electrolytic cell.
Japanese Laid-Open Patent Publication No. 2002-184386 describes an inspection apparatus for optically inspecting the connection state of each electrode plate 10 and the current collector plate 11 of the rechargeable battery electrode plate-connected structure. The inspection apparatus captures an image of the connection portion between each electrode plate 10 and the current collector plate 11 in the electrode plate-connected structure, analyzes the captured image, and quantitatively evaluates the connection strength of each fillet 12 to determine whether or not the connection state of each electrode plate 10 and the current collector plate 11 is satisfactory. A prior art method for optically inspecting the connection state will now be described with reference to FIG. 11. An electrode plate-connected structure 100 is arranged between an imaging device 101 and a lighting device 102. The lighting device 102 illuminates the electrode plate-connected structure 100 as the imaging device 101 captures an image of the connection portion between each electrode plate 10 and current collector plate 11. In this case, inspection light is transmitted through the interior of the electrode plate-connected structure 100 and received by the imaging device 101, which captures an image of the electrode plate-connected structure 100.